1. Field of the Invention
The present invention relates to a scanner and a scanning method for the scanner, and more particularly, to a scanner capable of selecting scanning positions and a scanning method for the scanner for preventing dust grains from affecting scanned images and for improving a scanning quality of the scanner.
2. Description of the Prior Art
Scanners are primary document processing devices in modern societies, particularly sheet-fed scanners, which are popular for scanning stacks of documents. Differing from the sheet-fed scanner, the flatbed scanner can merely scan one sheet of document in each scan, and it indicates a fact that after a first sheet of document is scanned, a second sheet of document cannot be scanned until the first sheet is removed or replaced, so that the flatbed scanner is troublesome in scanning a large number of documents. On the contrary, the sheet-fed scanner provides an automatic sheet-feeding mechanism, with which the sheet-fed scanner conveys a stack of sheets of documents one by one to a scanning position automatically and scans the stack of sheets consecutively. Therefore, the sheet-fed scanner is easy for usage, and saves much time of users.
However, for a sheet-fed scanner, or even for a flatbed equipped with an automatic document feeder, an interior scanning module is fixed at a same location for scanning documents. Therefore, when being scanned, sheets of documents are fed into the scanner one by one by the sheet feeder, and each sheet of document is moved across a scanning window, which is located corresponding to the scanning position of the scanning module. However, when such a scanner has dust grains on the scanning window, the dust grains are scanned along with the documents so that image data generated have unexpected lines, which do not exist on said documents. That is, the scanning quality of the scanner is affected by the dust grains.
Though decreasing the amount of dust grains around the scanner may reduce the effect of the dust grains, however, some tiny materials such as tiny dust grains, flakes, or hairs are hard to be removed and avoided. It is more troublesome when such tiny materials adhere to the under side of the scanning window. Moreover, the cleaner the surroundings for the manufacturing of the scanner are, the cost for the production of the scanner gets higher, and a scanner having a higher resolution requires cleaner surroundings. Instead of spending such a huge cost in cleaning surroundings for the manufacturing of the scanner, the scanning mechanism of the scanner is more worthy of being improved for refining the scanning quality.
Please refer to FIG. 1, which is a simplified diagram of a conventional sheet-fed scanner 100. The sheet-fed scanner 100 includes a housing 110, a sheet-in tray 115, a sheet-out tray 116, a stepper motor 130, a roller 125, a transparent platform 135, a light source 140, a memory 150, a control circuit 155, and a scanning module 145.
The sheet-in tray 115 is connected to the housing 110 for storing a stack of to-be-scanned documents 120. The sheet-out tray 116 is also connected to the housing 110 for storing a stack of scanned documents 121. The stepper motor 130 is disposed interior to the housing 110 for rotating the roller 125 to move the to-be-scanned documents 120 into the housing 110 one by one. The control circuit 155 is utilized for manipulating the scanner 100. The scanning module 145 is disposed interior to the scanner 100 for scanning the to-be-scanned documents 120 to generate image data of said to-be-scanned documents 120. The light source 140 provides light required in scans. The memory 150 is utilized for storing the generated image data. The scanning module 145 is located at a scanning position. When the roller 125 moves a sheet of the to-be-scanned documents 120 across the scanning position, the scanning module 145 scans the sheet of the to-be-scanned documents 120, and stores an image datum generated by scanning the sheet of the to-be-scanned documents 120 into the memory 150.
The scan procedure implemented on the sheet-fed scanner 100 includes steps as follows:
Step 00: Load the to-be-scanned documents 120 in the sheet-in tray 115 of the sheet-fed scanner 100.
Step 05: Initiate the scan procedure for the to-be-scanned documents 120.
Step 10: Control the stepper motor 130 to rotate the roller 125 for moving sheets of the to-be-scanned documents 120 to the transparent platform 135.
Step 15: Control the scanning module 145 with the control circuit 155 to scan sheets of the to-be-scanned documents 120 when the roller 125 moves the to-be-scanned documents 120 sheet by sheet across the scanning position, and store image data of the to-be-scanned documents 120 into the memory 150.
Step 20: Repeat Step 10 and Step 15 until all sheets of the to-be-scanned documents 120 are scanned.
In the scan procedure, the scanning module 145 scans the to-be-scanned documents 120 sheet by sheet at a same location, i.e., the scanning position of the scanning module 145 for scanning the to-be-scanned documents 120 is fixed. Therefore, when there are dust grains 180 at the scanning position of the scanning module 145 on the transparent platform 135, there are corresponding lines on the generated image data.
Please refer to FIG. 2, which is a diagram of an image datum 220 when there is a dust grain 180 at the under side of the transparent platform 135 of the sheet-fed scanner 100. As illustrated in FIG. 2, there is a line 280 on the image datum 220. The line 280 results from the fact that when a sheet of the to-be-scanned document 120 is moved across the transparent platform 135, the dust grain 180 keeps on preventing lights from passing through and results in a corresponding shadow in the scan. If the dust grain 180 is removed at the scanning position, the line 280 disappears too. Therefore, the scanning quality of the sheet-fed scanner 100 is severely affected by the dust grain 180 adhering to the transparent platform 135.